Babesia microti is an apicomplexan intraerythrocytic parasite that is the etiological agent of babesiosis. The host for Babesia microti is the white footed mouse, Peromyscus leucopus, although other small rodents are also susceptible to infection (Horner et al., 2000). The parasite is transmitted by the bite of a deer tick, Ixodes scapularis, which is endemic to the northeastern section of the United States (Anderson et al., 1991). Babesia spp. exists worldwide and Babesia microti is the most common cause of babesial infections in the United States. Babesiosis has been increasing in prevalence over the past thirty years and is an emergent zoonotic pathogen (Telford et al., 2004) that has increased concerns to the healthcare and diagnostic industries.
Babesia microti infection causes a malaria-like disease including malaise, chills, anemia, fatigue, fever and myalgia. Parasitemia levels appear to correlate with the severity of the disease. While the disease is frequently asymptomatic in healthy individuals, it is most severe in immuno-compromised patients. The time from disease transmission to manifestation ranges from one to six weeks or longer. Proper diagnosis of Babesia infection is necessary for the treatment of the disease.
Diagnosis of babesiosis is assessed by several different diagnostic methods including thin blood smear, PCR or serology (Persing et al., 1992; Krause et al., 1994). Blood smear detection is a specific method. Some patients may have a low parasitemia and thus can easily be missed in a smear. Thus, the screening method often yields false negatives. Molecular testing such as polymerase chain reaction (PCR) is a specific test with reported higher sensitivity. However, like blood smear, PCR can only detect current infections, and both of these tests cannot detect Babesia infections that have been recently cleared by the host immune system.
Serological diagnostic assay is a specific diagnostic test that can provide evidence for both recent and past infections by determining the antibody response. Current commercial serology tests involve the use of indirect immunofluorescent antibody assay (IFA). This assay is sensitive and specific, but is non-quantitative. It requires expensive fluorescent microscopy to read. In addition, the assay is subjective due to its dependence on the individuals who read the slides. IFA results are reported as titers relative to control samples.
Several groups have reported the identification of various Babesia proteins and genes that are speculated to encode immunogenic proteins. U.S. Pat. No. 4,596,707 discloses a soluble Babesia antigen isolated from Babesia-infected erythrocytes, with a MW of about 900,000. U.S. Pat. No. 5,209,929 discloses three substantially purified Babesia bigemina proteins having MWs of ˜58,000 Da, ˜55,000 Da and ˜45,000 Da. U.S. Pat. No. 5,273,884 discloses an antigen (W11C5) with a MW ˜160 kDa isolated from Babesia bovis. Using a peptide-based approach, U.S. Pat. No. 7,390,626 discloses an ELISA in detecting Babesia microti, Babsia bovie, and Babesia equi. 
U.S. Pat. No. 6,183,976 discloses a family of antigen isolated from Babesia microti. Using sonication to randomly shear genomic DNA isolated from infected hamster, a Babesia microti genomic expression library. Babesia microti-infected patient sera were used to screen for immuno-reactive positive clones. Seventeen antigens, referred to as BMN1-17, were reported. Nine of the isolated antigens belong to partial clones of BMN1-3, and contain a degenerate repeat of six amino acids. Another five antigens bear some homology to each other and contain a degenerate repeat of 32 amino acids. However, the sensitivity and specificity data relating ELISA on these antigens are not reported.
Ryan et al. (2001) describe the development of a Western blot in the diagnosis of recent and current infection with Babesia microti. This assay requires the presence of two or more bands to be considered positive and is reported to have high sensitivity and specificity. However, the Western blot assay is not commercially available, in part because the assay is tedious and time-consuming. However, to date, no assay has been developed commercially for the diagnostic use stemming from these studies.
There is a continuing need for a highly sensitive and specific serological assay for the detection of an antibody response for Babesia microti. The prior art methods have failed to solve a major goal in the diagnostics industry for this disorder for the past several decades.